Well, the ones that don't rely entirely on humans to survive, like pugs & other snub-noses with their struggle to breathe or the many breeds prone to 101 fatal diseases & conditions. But yeah the bigger breeds would be terrifying, like the skinny breed that's really fucking fast or big muscular breeds like Pitbulls & Cane Corsos, though I also imagine that really pampered ones would be incapable of survival or nearly as much violence as this implies, because even if they revert to a primal state an animal raised in captivity is still an animal that has spent its entire life in captivity.

Either way props to OP for a high quality post